That's probably what they're thinking. It makes little sense for the PLAAF to get a lot of FC-31s, since the FC-31s are going to be expensive and won't deliver the same capability as the J-20s. However, if Shenyang scores the PLANAF procurement, they have a guarantee of maybe 50-100 FC-31s. An EW / strike variant might also see carrier use, and an export variant means more orders.Very interesting. Four variants should make for a decently sized production run at the very least.
Shenyang, remember, does not want to go out of existence, and the PLA doesn't benefit from a Chengdu monopoly on Chinese fighters. While the PLAAF might not be able to sustain Shenyang, a combination of the PLAAF, PLANAF, and export markets might.